Brake fluid pressure control apparatus

ABSTRACT

The present invention relates to a brake fluid pressure control apparatus in which a casing contains a pump communication port separately from a master cylinder communication port. A spool is also provided which limits the communication between the pump communication port and the master cylinder communication port in a manner such that the discharge pressure from the pump is not added directly to the master cylinder. Additionally, in the intake and discharge sides of the pump, a bypass channel is provided. In this bypass channel, a relief valve is provided which allows the escape of pressure force to the intake side of the pump in the case when the pressure force between the discharge side of the pump and the flow control valve increases to a high pressure. Furthermore, because the brake fluid is normally designed to be discharged from the pump to the flow control valve at approximately a fixed flow rate by means of the relief valve, there is no return of brake fluid to the master cylinder via the flow control valve, and stroke fluctuations of the master cylinder can be eliminated. Additionally, the necessity for providing an orifice between a pump communication port and the master cylinder communication port disappears.

This application is a divisional of 07/904,988, filed Jun. 26, 1992, nowU.S. Pat. No. 5,312,175.

BACKGROUND OF THE INVENTION

The present invention relates to a brake fluid pressure adjustmentapparatus possessing antiskid control action for use in brakeapparatuses of vehicles, which, prevents locking of vehicle wheelsduring braking.

PRIOR ART

FIG. 12 shows a brake fluid pressure adjustment apparatus possessingantiskid control action for use in brake apparatuses of vehicles, whichprevents locking of the wheels during braking (Japanese PatentApplication First Publication No. Hei 1-297350; U.S. patent applicationNo. 4,988,148). This brake fluid pressure control apparatus 261 employsa flow control valve possessing a casing 258 and a spool 259. In casing258, a master cylinder communication port 251, a wheel cylindercommunication port 253, and a reservoir communication port 257 areprovided. Master cylinder communication port 251 is communicated to amaster cylinder 250, wheel cylinder communication port 253 iscommunicated to a wheel cylinder 252, and reservoir communication port257 is communicated to the intake side of pump 256 and reservoir 255 viafirst valve 254. Furthermore, pump 256 takes in and discharges brakefluid inside of the reservoir 255. Spool 259 is provided in a mannersuch that it is movable within casing 258.

Spool 259 of flow control valve 260 communicates master cylindercommunication port 251 and wheel cylinder communication port 253 duringnon-action of antiskid control. Additionally, spool 259 moves by meansof the difference in pressure created due to the opening of first valve254 at the time of pressure reduction during antiskid control, andlimits the communication of master cylinder communication port 251 andwheel cylinder communication port 253, while at the same time connectingwheel cylinder communication port 253 and reservoir 257. At the sametime, spool 259 supplies to wheel cylinder 252 brake fluid which isreturned by means of pump 256, through the closing of the aforementionedfirst valve 254 during repressurization.

Brake fluid pressure adjustment apparatus 261 is constructed in a mannersuch that at the time of repressurization of brake fluid pressure duringantiskid action, the pulsating motion generated by pump 256 and thestroke fluctuations (so-called "kick-back") created in master cylinder250 are both prevented. That is, the brake fluid discharged by pump 256,with no relation to master cylinder 250, passes via flow control valve260 at a fixed flow amount, flowing out towards wheel cylinder 252. As aresult, casing 258 possesses, individually, pump communication port 262connecting to the discharge side of pump 256. Additionally, duringantiskid control, spool 259 limits the communication between pumpcommunication port 262 and master cylinder communication port 251.Together with this, a channel 263, separate from flow control valve 260,is provided between master cylinder communication port 251 and pumpcommunication port 262 in a manner so that brake fluid is returned at afixed flow amount from pump 256 to master cylinder 250; in this channel263, an orifice 264 is provided. However, in the above-mentionedconstruction of brake fluid pressure adjustment apparatus 261, when theaforementioned orifice 264 between master cylinder communication port251 and pump communication port 262 is large, a large pump pulsation isimparted to master cylinder 250. Additionally, when orifice 264 is toosmall, there exist problems during manufacturing, such as increasedprocessing costs, as well as problems such as gum, mixed into the brakefluid, becoming clogged at orifice 264. Furthermore, orifice 264 variesthe flow amount of brake fluid returned to master cylinder 250 due tofluctuation in the discharge pressure of pump 256. As a result, a strokefluctuation is created by master cylinder 250. Therefore, in regard tothe above points, improvements have become necessary.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a brake fluidpressure adjustment apparatus which can, by means of elimination of theorifice provided between the master cylinder communication port and pumpcommunication port, be manufactured at a low cost, without theoccurrence of clogging of gum and the like, as well as in reality stopstroke fluctuations of the master cylinder.

In order to achieve the above objectives, the present invention, inorder to carry out antiskid-control of the vehicle, supplies a brakefluid pressure control apparatus to be provided on a brake fluidpressure control circuit for antiskid control of wheeled vehicles, thebrake fluid pressure control circuit including a brake pedal forinitiating braking of the wheels, a master cylinder for providing brakefluid pressure to the circuit, and wheel cylinders for providing brakefluid pressure to brakes of the wheels, the brake fluid pressure controlapparatus comprising:

a first valve which opens when brake fluid pressure decreases, andcloses when brake fluid pressure increases;

a reservoir for receiving brake fluid;

a pump having an intake side for taking in brake fluid from thereservoir, and an outlet side for discharging brake fluid;

a flow control valve communicating with the master cylinder, the wheelcylinder, the reservoir, and the pump, this flow control valvecontrolling the fluid flow so that the fluid pressure of the wheelcylinder undergoes pressure decrease and pressure increase; the flowcontrol valve comprising:

a casing comprising:

a master cylinder communication port communicating to the mastercylinder;

a wheel cylinder communication port communicating to the wheel cylinder;

a reservoir communication port communicating with the intake side of thepump and the reservoir via the first valve; and

a pump communication port which connects to the discharge side of saidpump;

a spool, provided as a movable element inside of the casing;

a spring which provides force to the spool in one direction;

wherein the spool, in a motionless state in which force is provided inone direction by the spring, connects the master cylinder communicationport and the wheel cylinder communication port;

and during brake fluid pressure decrease, moves by means of a differencein pressure generated on both sides by means of the opening of the firstvalve restricts the communication between the master cylindercommunication port and the wheel cylinder communication port, connectsthe wheel cylinder communication port and the reservoir communicationport, and restricts the communication between the pump communicationport and the master cylinder communication port;

the spool which, during brake fluid pressure decrease, when the firstvalve is in the open state, supplies brake fluid discharged from thepump from the pump communication port to the reservoir communicationport via the interior orifice at roughly a fixed flow amount;

and the spool, during brake fluid pressure increase, when the firstvalve returns to a closed condition, supplies brake fluid dischargedfrom the pump from the pump communication port to the wheel cylindercommunication port at roughly a fixed flow amount via interior orificeprovided on the interior portion;

first bypass channel which joins the intake side and discharge the ofsaid pump in a bypass manner; and

a relief valve provided in this first bypass channel, which, in the casewhen brake fluid pressure between the discharge side of the pump and theflow control valve exceeds a predetermined pressure, controls the flowamount of brake fluid to the flow control valve by means of allowingsurplus brake fluid pressure to escape to the intake side of said pump;whereby controlling the brake fluid pressure so as to prevent slippageof the wheels during braking.

With the construction of the present invention, the pump communicationport is individually communicated to the pump. Thus, during movement ofthe spool, the pressure discharge from the pump is not added directly tothe master cylinder due to this spool. That is, the communication of thepump communication port and the master cylinder communication port isrestricted. In this manner, when the communication of the mastercylinder and the pump is in a restricted state, the following actionsoccur.

When the brake fluid is discharged from the pump from the flow controlvalve, the relief valve provided on the bypass channel which bypassesthe intake and discharge sides of the pump allows for the release ofsurplus pressure to the intake side of the pump, in the case when thepressure between the discharge side of the pump and the pumpcommunication port. exceeds a predetermined pressure.

As a result, it is arranged so that, brake fluid is always discharged atan approximately fixed flow amount from the pump to the pumpcommunication port. The entire amount of this brake fluid passes throughthe flow control valve; for example, this brake fluid is supplied at afixed flow amount towards the wheel cylinder, and thus the return ofbrake fluid to the master cylinder does not occur. Furthermore,communication of the master cylinder communication port and the pumpcommunication port, via the orifice provided on a separate channel fromthe flow control valve, becomes unnecessary.

Consequently, by means of the brake fluid flowing through the flowcontrol valve from the pump at approximately a fixed flow amount, returnof the brake fluid to the master cylinder does not occur, andelimination of the stroke fluctuations of the master cylinder ispossible. Additionally, there is no need for a reciprocal communicationbetween the master cylinder communication port and the pumpcommunication port via an orifice provided on a separate channel fromthe flow control valve, and thus, the situation in which the gum mixedinto the brake fluid clogs at the orifice is not created, and thereliability is thereby increased. Furthermore, in the pump, there is noaction of a pressure burden over a fixed value, and due to this,fluctuations in the sound of the pump and in the sound of the motordriving the pump disappear, and thus discordant sounds from action canno longer be perceived by the ear. Together with this, because there isno longer a necessity of creating excessively large pressure above theopen valve pressure of the relief valve in the pump, a minimum necessarylimit for the driving force of the motor driving the pump is set, andthe weight and cost of the motor is thus decreased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an outline of the construction of a brakefluid pressure adjustment apparatus according to a first preferredembodiment.

FIG. 2 schematically shows an outline of the construction of a brakefluid pressure adjustment apparatus according to a second preferredembodiment.

FIG. 3 is a cross sectional view showing a relief valve of a brake fluidpressure adjustment apparatus according to a second preferredembodiment.

FIG. 4 schematically shows an outline of the construction of a brakefluid pressure adjustment apparatus according to a third preferredembodiment.

FIG. 5 schematically shows an outline of the construction of a brakefluid pressure adjustment apparatus according to a fourth preferredembodiment.

FIG. 6 schematically shows an outline of the construction of a brakefluid pressure adjustment apparatus according to the fifth preferredembodiment.

FIG. 7 schematically shows an outline of the construction of a brakefluid pressure adjustment apparatus according to a sixth preferredembodiment.

FIG. 8 schematically shows an outline of the construction of a flowcontrol valve and a first valve of a brake fluid pressure adjustmentapparatus according a seventh preferred embodiment.

FIG. 9 is a cross sectional view taken along the line X-X shown in FIG.8.

FIG. 10 is a constructional outline showing a modification of a brakefluid pressure adjustment apparatus according a seventh preferredembodiment.

FIG. 11 is a constructional outline showing a flow control valve and afirst valve of a brake fluid pressure adjustment apparatus according toan eighth preferred embodiment.

FIG. 12 is a constructional outline showing a prior art brake fluidpressure adjustment apparatus.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

In the following, a description of the brake fluid pressure adjustmentapparatus according to the first preferred embodiment of the presentinvention will be given with reference to FIG. 1. Furthermore,upper/lower parts of the figure have been abbreviated for convenience as"upper/lower" in the following description.

In the figure, master cylinder 1 is communicated to brake pedal 2, andin response to the pressing of this brake pedal 2, brake fluid pressureis generated. Wheel cylinder 3 brakes the wheel 4 of the vehicle bymeans of brake fluid pressure. A brake fluid pressure control circuit 5is also provided which is communicated between master cylinder 1 andwheel cylinder 3; in this brake fluid pressure control circuit 5, abrake fluid pressure control apparatus 6 is provided. This brake fluidpressure control apparatus 6 carries out antiskid control, that is, thisbrake fluid pressure control apparatus 6 lowers and raises the pressureof the brake fluid passing from master cylinder 1 to wheel cylinder 3 inresponse to the slip tendency of the vehicle wheel 4.

A flow control valve 8 is provided in a channel 7, within brake fluidpressure control circuit 5, which communicates to master cylinder 5.This flow control valve 8 houses casing 10. This casing 10 has acylindrically shaped cylinder portion 9 which extends in an up/downdirection; a plurality of ports are provided on this cylinder portion 9.

These aforementioned ports include master cylinder communication port11, wheel cylinder communication port 13, reservoir communication port14, and pump communication-port 15.

Master cylinder communication port 11 lies orthogonal to the axis ofcylinder portion 9, and is provided at a predetermined position,connecting to master cylinder 1 via channel 7.

Wheel cylinder communication port 13 is provided below the predetermineddistance of master cylinder communication port 11, and communicates towheel cylinder 3 via channel 12 of brake fluid pressure control circuit5.

Reservoir communication port 14 is provided in a predetermined positionat the lower portion of cylinder portion 9, along the direction of theaxis of cylinder portion 9.

Pump communication port 15 is provided opposite master cylindercommunication port 11 along the same axis.

Furthermore, the aforementioned wheel cylinder communication port 13 isformed from upper portion port 16 and lower portion port 17. Upperportion port 16 is provided parallel to master cylinder communicationport 11 at a distance less than the predetermined distance of mastercylinder communication port 11. The lower portion port 17 communicatesand lies parallel to upper portion port 16 on the outside of cylinderportion 9, and is provided in at a distance less than the predetermineddistance of upper portion port 16.

Reservoir communication port 14 of flow control valve 8 communicates tothe variable capacity reservoir 18 via channel 19 of brake fluidpressure control circuit 5, and an electromagnetic first valve 20 isprovided along channel 19 between flow control valve 8 and reservoir 18.

Furthermore, the aforementioned reservoir 18, in order to achieve thisvariable capacity function, includes a reservoir cylinder 21, areservoir piston 22 which is housed inside reservoir cylinder 21 as aslidable element, and a reservoir spring 23 which urges reservoir piston22 at a predetermined force. Additionally, pump communication port 15 offlow control valve 8 is communication to reservoir 18 via channel 24 ofbrake fluid pressure control circuit 5.

Along this channel 24, between flow control valve 8 and reservoir 18,pump 25 is provided. This pump 25 is comprised of pump main body 26,intake valve 27, and discharge valve 28. Pump main body 26 carries outintake and discharge functions by means of a driving motor. Intake valve27, provided between pump main body 26 and reservoir 18, allows for onlythe flow of brake fluid from reservoir 18 to pump main body 26.Discharge valve 28, provided between pump main body 26 and pumpcommunication port 15, allows for only the flow of brake fluid from pumpmain body 26 to pump communication port 15. This pump 25 is designedchiefly to intake brake fluid inside of reservoir 18 and discharge thisbrake fluid to pump communication port 15 of flow control valve 8.

Furthermore, inside of casing 10 of flow control valve 8, a solidcylindrically shaped spool 31 is inserted in a manner such that it canmove upwardly and downwardly. This spool 31 includes upper portionaperture 32, lower portion aperture 33, and interior orifice 34. Theupper portion aperture 32 is drilled centrally along the direction ofthe axle at a predetermined diameter, from the upper end portion ofspool 31 to the nearly center position which is predetermined. The lowerportion aperture 33 is formed at the same diameter as that of the axleand the upper portion 32, from the lower end portion of spool 31 to thenearly center position which is predetermined, and normally communicatesto reservoir communication port 14. Upper portion aperture 32 and lowerportion aperture 33 are communicated to each other at interior orifice34 which has a predetermined diameter which is smaller than either ofthe aforementioned apertures. Furthermore, at the lower end, an openingportion 35 of lower portion aperture 33 is designed at a predeterminedvalue greater than the diameter of the other portions. The upper portionof spring 36 is inserted into this opening portion 35. Spring 36provides a predetermined force to spool 31 in the upward direction.

When antiskid control is not being carried out, spool 31, by means ofthe force provided by spring 36, has its upper portion in contact withthe upper portion of cylinder portion 9, and enters a motionless state(the state shown in FIG. 1). In contrast, when electromagnetic firstvalve 20 opens, a difference in pressure from both sides is created ininterior orifice 34 by means of brake fluid inside of lower portionaperture 33 flowing to reservoir 18. By means of this difference inpressure, spool 31 moves downwards. This spring 36 is the springdescribed in claim 1.

Spool 31 includes first groove portion 37, first aperture 38, secondaperture 39, second groove portion 41, third aperture 42, third grooveportion 43, and fourth aperture 44.

First groove portion 37 is provided at the outer periphery of spool 31below a predetermined distance from the upper end, extending around theentire circumference, and possessing a predetermined width. Firstaperture 38 communicates first groove portion 37 and upper portionaperture 32. Second aperture 39 communicates first groove portion 37 andupper portion aperture 32. When spool 31 is in a motionless state, firstgroove portion 37 communicates master cylinder communication port 11 andpump communication port 15. During this time, master cylindercommunication port 11 and pump communication port 15 are communicateddirectly by means of first groove portion 37, and are communicated viafirst aperture 38, upper portion aperture 32, and second aperture 39.

Second groove portion 41 is provided at the periphery at a predetermineddistance from first groove portion 37, extending over the entirecircumference, and having a predetermined width. Third aperture 42communicates second groove portion 41 and upper portion aperture 32.When spool 31 is in a motionless state, upper portion aperture 32 andupper portion port 16 are communicated by means of second groove portion41 and third aperture 42; in contrast, when spool 31 is in a state ofmotion, the communication of upper portion aperture 32 and upper portionport 16 is cut off.

Third groove portion 43 is provided at the outer periphery of spool 31at a predetermined distance from second groove portion 41, extendingover the entire circumference, and possessing a predetermined width.Fourth aperture 44 communicates third groove portion 43 and lowerportion aperture 33. When spool 31 is in a motionless state, thecommunication of lower portion aperture 33 and lower portion part 17 iscut off by means of third groove portion 43 and fourth aperture 44; incontrast, when spool 31 is a state of motion, lower portion aperture 33and lower portion port 17 are communicated by means of third grooveportion 43 and fourth aperture

For the sake of convenience, first aperture 38 and second aperture 39have been described separately; however, because first groove 37 isprovided in spool 31, they may be considered as one aperture.

The portion between pump communication port 15 and discharge valve 28 onchannel 24 and the portion between electromagnetic first valve 20 andintake valve 27 on channel 19 are joined by first bypass channel 45.Along this first bypass channel 45, a relief valve 46 is provided. Thisrelief valve 46 is designed to open when the brake fluid pressurebetween discharge valve 28 and pump communication port 15 exceeds apredetermined value. When this relief valve 46 opens, the surplus brakefluid pressure escapes to the intake side of pump 25 from channel 24.

In the following, an explanation will be given in regard to the actionof brake fluid pressure control apparatus 1 according to the firstembodiment of the present invention.

To begin with, when antiskid control is in a nonactive state, spool 31of flow control valve 8, as shown in FIG. 1, communicates mastercylinder 1 and wheel cylinder 3 via master cylinder communication port11, first portion groove 37, first aperture 38, upper portion aperture32, third aperture 42, second groove portion 41, and upper portion port16. As a result, pressure is added to wheel cylinder 3 in response tothe pressing of brake pedal 2. When this occurs, the communication offourth aperture 44 and third groove portion 43 with all of the ports isdesigned to be cut off. Additionally, when brake pedal 2 is pressed, thebrake fluid pressure generated by master cylinder 1 is delivered to thedischarge side of pump 25 as well as relief valve 46 via pumpcommunication port 15 of flow control valve 8. However, the dischargevalve 28 is provided in pump 25, and additionally, the open valvepressure of relief valve 46 set at a predetermined high pressure thanthe brake fluid pressure generated by master cylinder 1. As a result,there is no delivery of brake fluid pressure to pump main body 26 viathe aforementioned communications.

Instructions are sent out from a control apparatus (not shown in thefigures) when a decision is made that the vehicle wheels have entered alocked tendency by means of information from a vehicle wheel speedsensor (also not shown in the figures). By means of these instructions,brake fluid pressure control apparatus 6 carries out thepressure-lowering action of antiskid control. That is, the brake fluidpressure between master cylinder 1 and wheel cylinder 3 is lowered. Whenthis occurs, the brake fluid inside the portion enclosed by lowerportion aperture 33 and cylinder portion 9, by means of opening ofelectromagnetic first valve 20, flows to reservoir 18, and as a result,a difference in pressure is generated on both sides of interior orifice34 of spool 31. By means of this difference in pressure, spool 31opposes the force of spring 36, and moves in a downward direction asseen in FIG. 1, cutting off the communication of second groove portion41 and upper portion port 16 together with restricting the communicationof master cylinder communication port 11 and upper portion port 16(i.e., reducing it to a minute communication, or cutting it offcompletely). At the same time, spool 31 communicates wheel cylinder 3and reservoir 18 via lower portion port 17, third groove portion 43,fourth aperture 44, lower aperture 33, and reservoir communication port14. As a result, the brake fluid inside of wheel cylinder 3 flows intoreservoir 18, and thus the brake fluid pressure of wheel cylinder 3 isreduced.

When this occurs, brake fluid is taken in from reservoir 18 and thendischarged to pump communication port 15 by means of the driving forceof pump 25. This brake fluid flows from pump communication port 15,passing through the interior of flow control valve 8, and flowing toreservoir 18. Furthermore, when in this condition, the communication ofmaster cylinder communication port 11 and pump communication port 15 isrestricted by spool 31. As a result, the pressure discharged from pump25 is not directly added to master cylinder 1. Furthermore, at the timeof readdition of pressure during antiskid control, brake fluid flowingfrom flow control valve 8 to reservoir 18 is stopped by the closing ofelectromagnetic first valve 20, and spool 31 moves slightly in theup/down direction of FIG. 1, by means of the pressure inside of lowerportion aperture 33. As a result, spool 31 supplies the brake fluidwhich until this time has been circulated by pump 25, from flow controlvalve 8 to wheel cylinder 3 via upper portion aperture 32, interiororifice 34, and fourth aperture 44. The amount of brake fluid flowing towheel cylinder 3 is more or less a fixed flow amount depending on theamount in the communication of first aperture 38 and master cylindercommunication port 11 and the amount in the communication of secondaperture 39 and pump communication port 15.

Similarly, during antiskid control, when the pressure in channel 24between pump 25 and flow control valve 8 exceeds a predeterminedpressure, relief valve 46 provided in first bypass channel 45 allows theescape of surplus pressure in channel 24 to the intake side of pump 25via first bypass channel 45. In this way, brake fluid at a fixedpressure is normally discharged from pump 25 towards pump communicationport 15. This brake fluid, passing through the interior of flow controlvalve 8, is supplied to wheel cylinder 3 or reservoir 18 in a fixed flowamount. Consequently, because the amount of brake fluid returning tomaster cylinder 1 is decreased, stroke fluctuations of master cylinder 1can be reduced.

Moreover, due to the release of surplus pressure by relief valve 46,there is no action in pump 25 for a pressure burden over a fixed value,and as a result, the rotation of pump 25 and the motor which drives thepump (not shown in the figures) can be maintained at a fixed rate. Inthis way, sounds which are discordant to the ear are not producedbecause fluctuations generating sounds as a result of usage of pump 25,as well as the motor which drives the pump, are phased out. Togetherwith this, the driving force of the motor driving pump can be set at aminimum necessary limit since the necessity of creating excessivelylarge pressure from open valve pressure of relief valve 46 is abolished.Due to the above, the cost as well as the weight of the motor arelikewise reduced.

Furthermore, it is no longer necessary for the orifice, provided on achannel separate from flow control valve 8, to connect master cylindercommunication port 11 and pump communication port 15; thus, unfavorablesituations in which the orifice acts as the source, do not occur (forexample, when gum mixed into the brake fluid is clogged at the orifice)and thus dependability can be improved.

Furthermore, it is desirable to set the open valve pressure of reliefvalve 46 to the maximum brake fluid pressure of the vehicle.

In the following, a brake fluid pressure adjustment apparatus accordingto the second embodiment of the present invention will be explained withreference to FIGS. 2 and 3. Furthermore, the chief difference betweenthe second embodiment in comparison to the first embodiment lies in therelief valve, thus the explanation will center around the parts whichare different: corresponding sections to the apparatus of the firstembodiment will be denoted by identical numbers; however, theseexplanations will be omitted.

The aforementioned brake fluid pressure adjustment apparatus 6 of thefirst embodiment is a fixed value set to the maximum brake fluidpressure of the vehicle which corresponds to the open valve pressure ofrelief valve 46. However, in the aforementioned construction, when thepressure of master cylinder 1 is low, there is the possibility that aquantity of brake fluid will return to master cylinder 1. Therefore, thebrake fluid pressure control apparatus of the second preferredembodiment further improves the aforementioned point.

To relief valve 47 of brake fluid pressure control apparatus 66according to the second embodiment, a branching channel 48 iscommunicated from channel 7 between master cylinder 1 and flow controlvalve 8, as shown in FIG. 2. This relief valve 47, as shown in FIG. 3,includes pump communication chamber 51 and master cylinder communicationchamber 52. Pump communication chamber 51 includes induction port 49,connecting to the discharge side of pump 25, and discharge port 50.Master cylinder communication chamber 52 is provided separately frompump communication chamber 51, and in master cylinder communicationchamber 52, communication port 53 is provided connecting to channel 48.

In the interior of pump communication chamber 51, valve element 55 isprovided. When this valve element 55 is seated onto seat portion 54,formed at the boundary portion of induction port 49 and the inner sideof pump communication chamber 51, this seat portion 54 is closed up.However, when valve element 55 moves toward the left in FIG. 3, by meansof brake fluid pressure introduced from induction port 49, the valveopens, and it becomes possible for brake fluid to flow to discharge port50. This valve element 55 houses, the tip portion 57, on the inductionport 49 side, of valve element spring 56, which provides force to theaforementioned valve element 55 in the direction corresponding to theright in FIG. 3.

Additionally, a piston 58 which is movable in the left/right directionsof FIG. 3 is housed inside of master cylinder communication chamber 52.This piston 58 can be urged toward the left in FIG. 3 by means of pistonspring 60 which is provided in between piston 58 and the end 59 ofmaster cylinder communication chamber 52 closest to pump communicationchamber 51. An axle portion 61 of piston 58 is inserted intocommunication aperture 62 which is provided in between pumpcommunication chamber 51 and master cylinder communication chamber 52.The other end 64 of the aforementioned valve element spring 56 inside ofpump communication chamber 51 is seated on end portion 63 of axleportion 61. Seal member 65, which seals communication aperture 62 whenpiston 58 is in the inserted condition, is provided in between mastercylinder communication chamber 52 and pump communication chamber 51.Furthermore, inside of master cylinder communication chamber 52, thechamber in which piston spring 60 is provided communicates with theatmosphere. The aforementioned valve element 55 and piston 58 comprisethe valve members, while valve element spring 56 and piston spring 60comprise the force men, pets.

Furthermore, the spring constants of valve element spring 56 and pistonspring 60 are set in a manner such that the discharge pressure of pump25 increases a given amount greater than the brake fluid pressuregenerated by master cylinder 1.

In this type of relief valve 47 construction, when the brake fluidpressure generated in channel 7 between master cylinder 1 and flowcontrol valve 8 flowing from channel 48 to relief valve 47, becomeslarge, piston 58 opposes the force of piston spring 60, and moves apredetermined distance in response to the amount of brake fluidpressure. Thus, this construction of relief valve 47 reduces valveelement spring 56 and increases the predetermined amount of valveopening pressure for valve element 55.

By controlling the opening valve pressure of relief valve 47 of brakefluid pressure control apparatus 66 in the above manner, the dischargepressure of pump 25 introduced in flow control valve 8 will correspondto the brake fluid pressure generated by master cylinder 1. As a result,in comparison to brake fluid pressure control apparatus 6 of the firstembodiment, the pressure burden on pump 25 and the motor which drivespump 25 can be further reduced; similarly, the amount of brake fluidreturning to master cylinder 1 can also be further reduced. Furthermore,the brake fluid of master cylinder 1 generated by the pressing of brakepedal 2 is designed to be delivered to the discharge side of pump 25 andrelief valve 47 via pump communication port 15 of flow control valve 8.However, a discharge valve 28 is provided in pump 25, and relief valve47 is designed so that the open valve pressure as stated above reaches afixed high pressure from the brake fluid pressure of master cylinder 1 .As a result, there is no delivery of brake fluid pressure to pump mainbody 26 and master cylinder 1 via discharge valve 28 and relief valve47.

In the following, a brake fluid pressure control apparatus according tothe third embodiment of the present invention will be explained withreference to FIG. 4. Furthermore, the main difference in the thirdembodiment with respect to the first embodiment and the secondembodiment lies principally within the relief valve, thus the followingexplanation will revolve around the portions which are different; thoseparts which are similar to the apparatus of the first and secondembodiments will be denoted using identical numbers, and theseexplanations will be omitted.

During antiskid control action of relief valves 46 and 47 of brake fluidpressure apparatuses 6 and 66, according to the above first and secondpreferred embodiments, when brake pedal 2 returns, brake fluid remainsinside reservoir 18; however, there is a possibility that this brakefluid will hinder the control qualities during the next antiskid controlaction. Therefore, brake fluid pressure control apparatus 67 accordingto the third embodiment prevents brake fluid from remaining insidereservoir 18 (without using pump 25), so that the control ability isunhindered in subsequent antiskid control action.

Furthermore, master cylinder 30 according to the third preferredembodiment is a tandem master cylinder, delivering brake fluid pressurethrough two brake fluid pressure control circuit systems 5A and 5B; bothcircuit systems are constructed identically; thus only one circuitsystem 5A is shown in the diagram.

Relief valve 68 according to the third embodiment has a generallycylindrical shaped housing 69 within which control port 70, dischargeport 71, and induction port 72 are provided. Control port 70 is providedat a predetermined position orthogonal to the axial direction of housing69. Discharge port 71 is parallel to control port 70 and is providedbelow a predetermined distance. Induction port 72 is provided along theaxial direction of the lower portion center of housing 69. Theaforementioned control port 70 is communicated to channel 7 betweenmaster cylinder 1 and flow control valve 8 through branched channel 48.Induction port 72 is joined to the communication point of channel 24 offirst bypass channel 45. Discharge port 71 is joined to thecommunication point of channel 19 of first bypass channel 45.Additionally, inside the peripheral portion at the upper end of housing69, an internal thread portion 73 is formed.

Inside of housing 69, the following are provided, in order, from thebottom to the top in FIG. 4: first member 74, second member 75, thirdmember 76, and fourth member 77.

First member 74 includes taper portion 78 and flange 79. Tapered portion78 is formed tapering towards the end which sets into induction port 72.Flange 79 is provided above tapered portion 78, and forms a circularplate. In the center of first member 74, a bore 80 is provided whichbores along the axial direction (comprising a portion of induction port72).

Second member 75 includes concave portion 81, valve element insert hole83, discharge aperture 84, seal groove 85, cup packing groove 86, andcommunication aperture 87. Concave portion 81 is provided at the lowerend of second member 75, and together with this, engages flange 79 offirst member 74.

Valve element insert hole 83, running along the axial direction of thecenter of second member 75, is opened a predetermined depth from thebottom, and houses valve element 82, which will be explained hereinafterin a manner so that valve 82 is movable. Discharge aperture 84 isprovided at a position approximately equal to the height of dischargeport 71 of housing 69. Seal groove 85 is provided at a predeterminedposition on the outer periphery of second member 75. Cup packing groove86 is provided at a predetermined diameter and a predetermined depthfrom the upper portion of second member 75 running along the axialdirection. Communication aperture 87 communicates cup packing groove 86and valve element insert hole 83 and thus is constructed having apredetermined diameter smaller than the aforementioned diameters.

Third members 76 include engagement convex portion 88, control aperture89, bore 90, insert opening 92, and seal groove 89a. Engagement convexportion 88 is provided at the lower end of third member 76 along theaxial direction, and engages the upper portion of the aforementionedsecond member 75. Control aperture 89 is provided at a position which isa predetermined distance above engagement convex portion 88 of thirdmember 76, at a height approximately equal to that of control port 70.Bore 90 communicates control aperture 89 and engagement convex portion88, and thus possesses a predetermined diameter. Insert opening 92 isprovided having a predetermined depth above and orthogonal to controlaperture 89. One end of piston spring 91 is inserted into this insertopening 92. Seal groove 89a is provided above control aperture 89 on theperipheral portion of third member 76.

At the periphery portion of fourth member 77, an external thread portion93 is constructed which screws into internal thread portion 73 ofhousing 69. By means of external thread portion 93 screwing intointernal thread portion 73, first member 74 is set onto induction port72 of housing 69, and in this state, predetermined portions of firstmember 74, second member 75, third member 76, and fourth member 77, eachrespectively engage or come into contact (the configuration shown inFIG. 4).

Additionally, in valve element insert hole 83 of second member 75, inthe engaged condition with first member 74, a valve element 82 formedfrom a globular shaped steel sphere is provided at the lower end. At theupper end of this valve element 82, a valve element spring 94 isprovided which provides a predetermined force to valve element 82 in thedirection to close off bore 80. Furthermore, the open valve pressure ofthis valve element 82 is greater than the pressure of master cylinder 1introduced from channel 48 (that is, the pressure of master cylinder 1added, along the axial direction, to insert portion 96 of piston 95 tobe explained hereinafter) by only the predetermined force provided bypiston spring 91 (to be explained hereinafter) and valve element spring94.

In addition, a piston 95 is inserted into communication aperture 87 ofsecond member 75 in a manner such that it is movable over apredetermined amount. Moreover, in between communication aperture 87 andpiston 95, there is a space. This piston 95 comprises, from the bottom,in order: tip portion 97, axle portion 98, and insert portion 96. Tipportion 97 is formed so that it tapers toward the end. Insert portion 96is inserted into one end of piston spring 91 (to be mentionedhereinafter). Piston spring 91 provides a predetermined force and isprovided in between insert portion 96 of piston 95, and insert opening92 of third member 76. It is designed so that by means of the forceprovided by piston spring 91, tip portion 97 of piston 95 first comes incontact with valve element 82, and then further urges valve element 92,urging it towards the direction of induction port 72. Additionally, aseal member 99 is provided in seal groove 85 of second member 75, whichis supported in between seal groove 85 and housing 69.

In the air space formed by cup packing groove 86 and piston 95 of thesecond member 75, a cup packing 100 with an approximately U-shaped crosssection with its curved side facing downward is inserted. This cuppacking 100, in the case when fluid pressure of master cylindercommunication chamber 101 is greater than the fluid pressure of pumpcommunication chamber 102 (both to be described hereinafter), widens,cutting off the communication of master cylinder communication chamber101 and pump communication chamber 102. In contrast, when the fluidpressure of master cylinder communication chamber 101 is lower than thefluid pressure of pump communication chamber 102, this cup packing 100allows the flow of brake fluid from pump communication chamber 102 tomaster cylinder communication chamber 101 via communication aperture 87,in the state in which piston 95 is inserted.

Additionally, seal member 103 is provided in seal groove 89a of thirdmember 76. This seal member 103 is supported between third member 76 andhousing 69.

Furthermore, the above-mentioned discharge aperture 84 and valve elementinsert hole 83 principally comprise pump communication chamber 102 whichcommunicates to pump 25 and is provided inside of housing 69. Controlaperture 89 and cup packing groove 86 principally comprise mastercylinder communication chamber 101 which communicates to master cylinder1 and is provided inside of housing 69. Valve element 82 and piston 95comprise the valve member. Piston spring 91 and valve element spring 94comprise the urging member. Channel 48, master cylinder communicationchamber 101, communication aperture 87 and pump communication chamber101 principally comprise the second bypass channel.

In the condition shown in FIG. 4, flow control valve 8 increases thepressure of wheel cylinder 3 in response to the pressing of brake pedal2, during normal action.

Similarly, as in the first embodiment, when antiskid control action isentered, pump 25 enters a driving state and the brake fluid dischargedfrom this pump 25 is controlled at a predetermined high level valuegreater than the brake fluid pressure generated by master cylinder 1 bymeans of relief valve 68, and is delivered to pump communication port 15of flow control valve 8. That is, the pressure of master cylinder 1 isintroduced to master cylinder communication chamber 101 from controlport 70 of relief valve 68 via channel 48, and this pressure is designedto act on insert portion 96 of piston 95 along the axial direction.Consequently, the pressure from master cylinder 1, as well as forceprovided by piston spring 91, are designed to act on piston 95. Thepressure from master cylinder 1, force provided by piston spring 91, aswell as force provided by valve element spring 94, are all designed toact on valve element 82, which is set in contact with tip portion 97 ofpiston 95. When the brake fluid pressure discharged from pump 25 to acton valve element 82 rises above the combined force of the aforementionedpressure force from master cylinder 1, driving force from piston spring91 and driving force from valve element spring 94, relief valve 68 opensinduction port 72, allowing surplus pressure to escape to the intakeside of pump 25 via discharge port 71 and first bypass channel 45.Consequently, the brake fluid pressure delivered to flow control valve 8is controlled at a predetermined high pressure level greater than thatfrom the pressure force from master cylinder 1 (combining the drivingforce provided by piston spring 91 and valve element spring 94). As aresult, using a concrete example, when the pressure force from mastercylinder 1 is at a comparatively low level, because the open valve ofrelief valve 68 is low, relief valve 68 opens easily, and brake fluidescapes to the intake side of pump 25. In contrast, when the pressureforce of master cylinder 1 is high, because the open valve pressure ofrelief valve 68 is high, relief valve 68 does not open easily, and thebrake fluid does not easily escape to the intake side of pump 25, inthis manner, due to the approximately linear fluctuations of the openvalve pressure of relief valve 68 in response to the pressure force ofmaster cylinder 1, approximately a fixed flow amount of brake fluid canflow from pump 25 towards flow control valve 8. As a result, the brakefluid amount returning to master cylinder 1 becomes approximately fixed,and pedal kickback is reduced.

During antiskid control, in the condition when brake fluid is inside ofreservoir 18, when the pressing of brake pedal 2 becomes weaker, and thepressure force of master cylinder 1 decreases, the pressure force ofmaster cylinder communication chamber 101 of relief valve 68 decreasesto a pressure force level less than that of pump communication port 102.In this way, cup packing 100 removes the shutting of communicationaperture 87 in the state with piston 95 inserted therein. The brakefluid inside of reservoir 18 is designed to return to master cylinder 1from reservoir 18 via first bypass channel 45, discharge port 71 ofrelief valve 68, pump communication chamber 102, communication aperture87, master cylinder communication chamber 101, control port 70, andchannel 48. As a result, return of the brake fluid inside reservoir 18to master cylinder 1 can be accomplished without activating pump 25.Consequently, there is no transfer of harmful effects on control abilityduring subsequent antiskid control action. Additionally, because it isunnecessary to drive pump 25 during times other than antiskid controlaction, uncomfortable sensations (generated by the usage noise of pump25) can be eliminated. Furthermore, in the aforementioned manner, valvemember of relief valve 68 is not constructed from piston 95 and globularshaped valve element 82, but construction as a unitary body is possible.However, generally globular shaped steel spheres can be used as valves82 requiring accuracy, by means of separate body construction, and as aresult, manufacturing costs can be lowered. Additionally, it is ofcourse possible to form a construction in which piston 95 and valveelement 82 are urged, by means of piston spring 91 and valve elementspring 94, as a single body, and not individually. However, by forming aconstruction which by which force is provided to these separately,because a smaller force can be applied when the aforementioned areseparated rather than united, the construction can be made more compact.Additionally, because it becomes possible for piston 95 to be returnedto its normal fixed position, unfavorable situations from failing of thebrake pedal can be prevented.

In the following, the fourth embodiment of the present invention will beexplained with reference to FIG. 5. Furthermore, in this fourthembodiment, the main difference in regard to the above third embodimentlies within relief-valve; thus the following description willconcentrate mainly on portions which are different; those portions whichare the same as in the above third embodiment will be denoted byidentical numbers and description thereof will be omitted. Additionally,as in the third embodiment, the brake fluid pressure control apparatusof the fourth embodiment contains two brake fluid pressure controlcircuit systems 5A and 5B which are of approximately the sameconstruction; therefore, only one circuit system 5A is shown andexplained; in regard to the other circuit system 5B, only portionsrequiring additional explanation are shown in the figure and explained.

Pump main body 26 of pump 25 in brake fluid pressure control circuitsystem 5A according to the fourth embodiment, is designed to be driventogether with pump main body 26 of pump 25 provided in the other circuitsystem 5B, by means of the same motor 105 and cam 106 (as shown by thedotted line in FIG. 5). It is designed so that when pump main body 26 ofcircuit system A takes in brake fluid, pump main body 26 of the othercircuit system 5B discharges brake fluid; similarly, when pump main body26 of circuit system 5A discharges brake fluid, pump main body ofcircuit system 5B takes in brake fluid. Similarly, in brake fluidpressure control apparatus 104 according to the fourth embodiment, arelief valve 107 is provided which allows escape of pressure force tothe intake side of pump 25 in the case when the pressure force inbetween pump 25 and pump communication port 15 of first bypass channel45 increases to a pressure greater than a predetermined pressure.

Relief valve 107, according to the fourth embodiment, includes pumpcommunication chamber 110, master cylinder communication chamber 112,seal chamber 113, system communication chamber 115, and communicationaperture 116. Pump communication chamber 110 includes induction port 108which communicates to the discharging side of pump 25 and discharge port109 which communicates to the intake side of pump 25. Master cylindercommunication chamber 112 includes return port 111 which communicates tomaster cylinder 1 of system 5A. Master cylinder communication chamber112 is provided in parallel above and separated from pump communicationchamber 110. Seal chamber 113 is provided in parallel, above andseparated from master cylinder communication chamber 112. Systemcommunication chamber 115 is provided in parallel, above and separatedfrom seal chamber 113, and contains control port 114 which communicatesto master cylinder 1 of system 5B. Communication aperture 116 penetratesthrough pump communication chamber 110, master cylinder communicationchamber 112, seal chamber 113, and system communication chamber 115. Inthis communication aperture 116, a cylindrically shaped piston 117,which can move a predetermined amount upwards/downwards, fittinglyinserted.

A spherical valve element 119 is provided in the aforementioned pumpcommunication chamber 110. This valve element 119 shuts off inductionport 108 when seated upon seat portion 118 at the boundary portion ofinduction port 108 and the inner part of pump communication chamber 110.In contrast, valve element 119, when the brake fluid pressure introducedto induction port 108 is greater than a predetermined value, moves inthe upward direction, thereby opening the valve. In this way, inductionport 108 is opened, and it becomes possible for brake fluid to flow tothe intake side of pump 25 via discharge port 109. In between this valveelement 119 and the wall face 110a of pump communication chamber 110, avalve element spring 120, which drives valve element 119 in the downwarddirection, is provided. Similarly, the lower end of piston 117 restsupon valve element 119. Furthermore, the open valve pressure of thisvalve element 119 is greater than the pressure force of master cylinder1 which is added to the upper tip portion of piston 117 introduced fromchannel 121 to be described hereinafter, by the predetermined quantityof force from valve element spring 120. Furthermore, the aforementionedpiston 117 and valve element 119 comprise the valve member, while valveelement spring 120 comprises the urging force member.

Cup packing 122 is inserted into the lower part of master cylinder 112.At the upper portion of this cup packing 122 of master cylindercommunication chamber 112, a return port 111 is provided connecting tochannel 48. Cup packing 122 works in the same way as cup packing 100 inthe aforementioned third embodiment. Channel 48, master cylinder 112,communication aperture 116, and pump communication chandler 110principally comprise second bypass channel.

In the aforementioned seal chamber 113, a seal ring 123 is provided. Bymeans of this seal ring 123, the communication of master cylindercommunication chamber 112 and system communication chamber 115 is cutoff.

By means of the brake fluid pressure control apparatus according to thefourth embodiment, during antiskid control, when pump 25 of system 5A,in order to discharge the brake fluid, moves from a maximum intakeposition to a maximum discharge position, pump 25 of system 5B, in orderto take in the brake fluid, moves from a maximum discharge position to amaximum intake position. As a result, the brake fluid pressure of mastercylinder 1 of system 5B, delivered via channel 121 to act on the uppertip portion of piston 117 of relief valve 107 in system 5A, has atendency to decrease. In this way, relief valve 107 of system 5Adecreases open valve pressure in response to rising of dischargepressure of pump 25 of the same system, gradually increasing the openvalve amount as well as the brake fluid amount escaping to the intakeside of pump 25. In contrast, when pump 25 of this system 5A, in orderto take in brake fluid, moves from the maximum discharge position to themaximum intake position, pump 25 of system 5B, in order to dischargebrake fluid, moves from a maximum intake position to a maximum dischargeposition; as a result, the brake fluid pressure of master cylinder 1 ofsystem 5B delivered via channel 121 to act on the tip portion of piston117 of relief valve 107 in system 5A, has a tendency to rise. In thisway, relief valve 107 of system 5A increases open valve pressure inresponse to the lowering of discharge pressure of pump 25 of the samesystem, and gradually decreases the open valve amount as well as theamount of brake fluid escaping to the intake side of pump 25. In doingthis, the pulsation of the brake fluid discharged to pump communicationport 15 of flow control valve 8 is reduced. Furthermore, system 5B alsofollows the same procedure. Consequently, by virtue of brake fluidpressure control apparatus 104, using the pulsations of both pumps 25 ofboth systems 5A and 5B, possessing reversed intake and discharge phases,the pulsations of each pump 25 cancel each other out.

Consequently, stroke fluctuations of master cylinder 1 as well asso-called "pedal kickback" can be further effectively reduced, andunpleasant sensations generated by means of the pump pulsations, such asusage sounds, can also be decreased. Moreover, this simple constructioncontains few elements, and thus can be constructed at a low cost. In theaforementioned explanation, an example is give in which pump 25 ofsystem 5A and pump 25 of system 5B had completely reversed intake anddischarge phases. However, good results can also be obtained with aslight difference between these, i.e., non-complete reversal.

In the following, the fifth embodiment of the present invention will beexplained with reference to FIG. 6. Furthermore, with respect to theaforementioned first embodiment, the fifth embodiment differs primarilyin the relief valve, thus this explanation will focus on differentportions, with portions similar to that of the aforementioned firstembodiment being denoted by identical numbers without explanations.

In brake fluid pressure control apparatus 125 of the fifth embodiment,second bypass channel 126 is provided with communicates channel 24,between pump communication port 15 and discharge valve 28, and mastercylinder 1 in a bypass manner. In first bypass channel 45 and secondbypass channel 126, valve mechanism 129 is provided. This valvemechanism 129 is a unitary body constructed from relief valve 127 (whichallows surplus discharge pressure from pump 25 to escape to reservoir18) and control valve 128 (which closes when fluid pressure of mastercylinder 1 from braking becomes high, and opens when fluid pressure ofmaster cylinder released from braking lowers).

In this valve mechanism 129, pump communication chamber 130, sealchamber 131, control chamber 132, valve chamber 133, communicationaperture 134, and bore 135 (one portion of second bypass channel 126)are provided. Seal chamber 131 is provided separated from pumpcommunication chamber 130. Control chamber 132 is provided separated onthe opposite side of seal chamber 131 with respect to pump communicationchamber 130. Valve chamber 133 is also provided separated on theopposite side of control chamber 132 with respect to seal chamber 131.Communication aperture 134 penetrates through pump communication chamber130, seal chamber 131, and control chamber 132. Bore 135 reciprocallycommunicates control chamber 132 and valve chamber 133. Furthermore,pump communication chamber 130, seal chamber 131, control chamber 132,valve chamber 133, communication aperture 134 and bore 135 are allarranged on the same axis.

Pump communication chamber 130 contains induction port 136 and dischargeport 137. Induction port 136 is provided on the same axis on theopposite side of pump communication chamber 130 with respect to sealchamber 131, and communicates to channel 24 in between second bypasschannel 126 and discharge valve 28. Discharge port 137 is providedorthogonal to pump communication chamber 130, and communicates toreservoir 28 of first bypass channel 45.

Control chamber 132 is constructed from small diameter chamber 138 andlarge diameter chamber 139 which has a predetermined diameter largerthan small diameter chamber 138. Small diameter chamber 138 is providedcloser to seal chamber 131 than large diameter chamber 139. Largediameter chamber 139 is provided on the side of small diameter chamber138 opposite that facing seal chamber 131. In large diameter chamber139, control port 140 and flow control valve communication port 141 areprovided. Control port 140 is provided in the orthogonal direction tothe axis of large diameter chamber 139 on the side of large diameterchamber 139 opposite that of small diameter chamber 138. This controlport 140 communicates to master cylinder 1. Flow control valvecommunication port 141 is provided opposite to control port 140; thisflow control valve communication port 141 communicates to mastercylinder communication port 11 of flow control valve 8.

In valve chamber 133, valve chamber port 142 is provided. Valve chamberport 142 is provided in the direction orthogonal to the axis of valvechamber 133, and this valve chamber port 142 communicates to thedischarge side of pump 25 via second bypass channel 126.

Valve element 143 possessing a smaller diameter than that of pumpcommunication chamber 130 is inserted inside pump communication chamber130. On this valve element 143, a valve part 144 is provided on theinduction port 136 side which allows the closing off of this inductionport 136. On the opposite side of valve element 143, in relation tovalve part 144, spring insert hole 145 is provided. Valve element spring146, providing a predetermined force, is set upon one end of bottomportion 147, and is inserted into spring insert hole 145.

Control piston 148 is inserted into communication aperture 134 andcontrol chamber 132. On this control piston 148 are provided axleportion 149, piston portion 150, contact portion 154, and rod portion156. Axle portion 149 is inserted into communication aperture 134, andtogether with this, one end of valve element spring 146 is inserted intothe tip portion nearest pump communication chamber 130. Piston 150 isprovided on the axle portion 149 side closest to valve chamber 133; thispiston portion 150 has a predetermined diameter larger than that of axleportion 149, and is fittingly inserted into large diameter chamber 139of control chamber 132 in a manner such that it is movable. In betweenpiston portion 150 and the end portion 151 of control chamber 132, onthe seal chandler 131 side, a spring 152 providing a predetermined forceis provided. Contact portion 154 is provided on the side of pistonportion 150 opposite that of axle portion 149. This contact portion 154can rest on end portion 153 of control chamber 132 on the valve chamber133 side without closing off bore 135. Rod portion 156 is provided onthe side of contact portion 154 opposite to that of piston 150. This rodportion 156 is constructed with a diameter smaller than that of bore135, and is responsible for the opening and closing of control valveelement 155 (to described hereinafter) of valve chamber 133.Furthermore, at the outer peripheral portion of piston portion 150 ofcontrol piston 148, a piston seal 157 is provided which prevents leakageof brake fluid passing over the aforementioned piston portion 150.

In valve chamber 133, control valve element 155, which can close bore135, is provided. In between control valve element 155 and the endportion 158 of valve chamber 133 opposite bore 135, spring 159, whichprovides a predetermined force, is provided. In seal chamber 131, sealmember 160 is provided which prevents leakage of brake fluid of pumpcommunication chamber 130 into small diameter chamber 138 viacommunication aperture 134 with axle portion 149 inserted.

Furthermore, the above valve element 143, valve element spring 146 andcontrol piston 148 principally comprise relief valve 127, while controlpiston 148, spring 152, spring 159, and control valve element 155principally comprise control valve 128.

By means of brake fluid pressure control apparatus 125 of the aboveconstruction, as shown in FIG. 6, in the condition in which braking isnot being carried out, control piston 148 of valve mechanism 129, bymeans of the force provided by spring 152, sets contact portion 154 ontothe end portion 153 of control chamber 132 facing valve chamber 133, andstops . In this manner, rod portion 156 of control piston 148 opposesthe force of spring 159, and urges control valve element 155 to move inthe direction opposite that of control chamber 132, opening up bore 135.Additionally, valve element 143 enters a condition in which it movestowards the induction port 136.

After moving from the aforementioned condition to a braking condition,when brake fluid pressure is generated from the master cylinder 1, thisfluid pressure of master cylinder 1 passes through control port 140,flows into control chamber 132, and acts on piston portion 150 ofcontrol piston 148. Together with this, the fluid pressure from mastercylinder 1 passes through flow control valve communication port 141 andis delivered to master cylinder communication port 11 of flow controlvalve 8. Similarly, by means of the aforementioned brake fluid pressureacting on piston portion 150, control piston 148 opposes the forceprovided by spring 151, moves in the direction of pump communicationchamber 130, and contacts step portion 161 between large diameterchamber 139 and small diameter chamber 138. As a result, contact betweencontrol valve element 155 and rod portion 156 of control piston 148 isreleased, and control valve element 155 closes bore 135 by means of theforce provided by spring 159. In contrast, by means of moving axleportion 149 of the aforementioned control piston 148, valve elementspring 146 is compressed, and by means of this compression of valveelement spring 146, valve element 143 is designed to maintain inductionport 136 in a closed state.

In this condition, in a case of antiskid control action, when thedischarge pressure of pump 25, which is greater than the force providedby the aforementioned compression of valve element spring 146, acts onvalve element 143, this valve element 143 opposes the force of valveelement spring 146, moves in the direction of control chamber 132, andopens up induction port 136. In this manner, the surplus dischargepressure of pump 25 is allowed to escape to reservoir 18 via firstbypass channel 45. Additionally, the discharge pressure of pump 25delivered to pump communication port 15 is designed to be controlled atapproximately a fixed rate. On the other hand, the discharge pressure ofpump 25 at this time is also designed to be delivered to valve chamber133 via second bypass channel 126. However, because bore 135 of valvechamber 133 is closed off by means of control valve element 155, thereis no delivery of this discharge pressure to master chamber 1 via secondbypass channel 126.

During this above antiskid control, after braking is released, when thefluid pressure of master cylinder 1 lowers, the fluid pressure to act onpiston portion 150 is designed to also lower. As a result, as shown inFIG. 6, control piston 150 moves towards valve chamber 133 by means ofthe force provided by spring 152, and sets its contact portion 154 incontact with end portion 153. In this way, control valve element 155opposes spring 159, and moves in the direction opposite that of controlchamber 132 opening up bore 135. As a result of this, the fluidremaining inside reservoir 18 discharged/taken in from pump 25 isdesigned to return directly to master cylinder 1 via second bypasschannel 126. Consequently, during antiskid control, in the case whenbraking is released, because the brake fluid discharged to flow controlvalve 8 disappears, the brake fluid flowing to wheel cylinder 3 alsodisappears. Therefore, there is no occurrence of the overshootphenomenon, and fluid pressure of wheel cylinder 3 is rapidly reduced inresponse to release of braking .

In the following, a brake fluid pressure control apparatus according tothe sixth embodiment of the present invention will be explained withreference to FIG. 7. Furthermore, in regards to the fifth embodiment,the sixth embodiment differs primarily in that the open valve pressureof the relief valve is arranged to follow the fluid pressure of channel7 generated by the master cylinder; additionally, the relief valve andthe control valve, are individually constructed. The followingexplanation will thus center around the portions which are different.

In brake fluid pressure control apparatus 163 according to the sixthembodiment, as in the fifth embodiment, first bypass channel 45(connecting in a bypass manner the discharging side of pump 25 andreservoir 18) and second bypass channel 126 (connecting in a bypassmanner channel 24 between pump communication port 15 and discharge valve28 and master cylinder 1) are provided.

In first bypass channel 45, a relief valve 164 is provided which will bedescribed below.

In this relief valve there are provided pump communication chamber 165,seal chamber 166, master cylinder communication chamber 167, andcommunication aperture 168. Seal chamber 166 is provided separated frompump communication chamber 165. Master cylinder 167 is provided on theside of seal chamber 166 opposite that of pump communication chamber165. Communication aperture 168 penetrates through pump communicationchamber 165, seal chamber 166, and master cylinder communication chamber167. Furthermore, pump communication chamber 165, seal chamber 166,master cylinder communication chamber 167, and communication aperture168 are all arranged in a straight line.

Pump communication chamber 165 contains induction port 169 and dischargeport 170. Induction port 169 is provided on the side of pumpcommunication chamber 165 opposite that of seal chamber 166, lying ofthe same axis as that of pump communication chamber 165, and connectingto discharge side of pump 25 of first bypass channel 45. Discharge port170 is provided orthogonal to pump communication chamber 165.

Master cylinder communication chamber 167 contains control port 171 andcoupling port 172 . Control port 171 in a direction orthogonal to theaxis of master cylinder communication chamber 167, and communicates tomaster cylinder 1. Coupling port 172 is provided on the side of mastercylinder communication chamber 167 opposite that of control port 171.

Inside pump communication chamber 165, valve element 173 which can closeoff induction port 169, is provided. In between this valve element 173and the end portion 177 of pump communication chamber 165 closest toseal chamber 166, a valve element spring 174 is provided which providesa predetermined force.

Into communication aperture 168, a piston 175, one tip of which is incontact with valve element 173 inside pump communication chamber 165,and the other tip of which projects out into master cylindercommunication chamber 167, is inserted.

Additionally, in seal chamber 166, a seal member 176 is provided whichseals communication aperture 168 with piston 175 inserted therein.

Furthermore, the aforementioned valve element and piston 175 comprisethe valve member, while valve element spring 174 comprises the forcemember.

On the other hand, a control valve 178 is provided in second bypasscircuit 126 which closes when the fluid pressure of master cylinder 1from braking increases, and opens when fluid pressure of master cylinder1 decreases following release of braking.

In the following, this control valve 178 will be explained. In thiscontrol valve 178 are provided valve chamber 179, control chamber 180,and bore 181 (the portion of second bypass circuit 126). Control chamber180 is provided separated from valve chamber 179. Bore 181 is providedbetween valve chamber 179 and control chamber 180, connecting the twochambers. Furthermore, valve chamber 179, control chamber 180, and bore181 are all arranged on the same axis.

In valve chamber 179, valve chamber port 182 is provided. This valvechamber port 182 is provided on the same axis as valve chamber 179 onthe side opposite that of control chamber 178, and communicates to thedischarge side of pump 25 of second bypass circuit 126. Control chamber180 is constructed from small diameter chamber 183, large diameterchamber 184, and communication chamber 185. Large diameter chamber 184is provided on the valve chamber 179 side of small diameter chamber 183and is formed at a predetermined diameter greater than that of smalldiameter chamber 183. Communication chamber 185 is provided on the valvechamber 179 side of large diameter chamber 184, and is formed at apredetermined diameter smaller than that of large chamber 184;similarly, at the juncture of communication chamber 185 and bore 181, aflow control valve communication port 186 is provided in the orthogonaldirection to the axis of the aforementioned communication chamber 185.This flow control valve communication port 186 communicates to mastercylinder communication chamber 11 of flow control valve 8 .Additionally, the aforementioned communication port 172 is communicatedto the opposite side of flow control valve communication port 186.

Inside valve chamber 179, control valve element 187 is provided whichcan close up bore 181. In between this control valve element 187 and endportion 188 of valve chamber 179 on the valve chamber port 182 side, aspring 189 which provides a predetermined force is provided.

Control piston 190 is inserted into control chamber 178 and bore 181.This control piston 190 has a rod portion 191, coupling portion 192,piston portion 193 and axle portion 194. Rod portion 191 is formed at adiameter smaller than bore 181, and can be inserted into bore 181 aswell as set in contact with control valve element 187. Coupling portion192 is provided on the side of rod portion 191 opposite that of valvechamber 179, and is constructed at a diameter smaller than that ofcommunication chamber 185. Piston portion 193 is provided on the side ofcoupling portion 192 opposite that of valve chamber 179, and is insertedinto large diameter chamber 184 in a manner so that it is movable. Axleportion 194 is provided on the side of piston portion 193 opposite thatof valve chamber 179, and is formed at a diameter smaller than that ofsmall diameter chamber 183. Furthermore, in between piston portion 193and end portion 195 of small diameter chamber 183 opposite that of valvechamber 179, a spring 196 is provided, on the inner side of which axleportion 194 is inserted, provides a predetermined force. Furthermore, onthe periphery of piston portion 193 of control piston 190, a piston seal197 is provided which prevents leakage of brake fluid via large diameterchamber 184 with piston portion 193 inserted therein.

In the condition in which braking is not being carried out, as shown inFIG. 7, control piston 190 of control valve 178, by means of the forceprovided by spring 196, places piston portion 193 in contact with stepportion 198 in between large diameter chamber 184 and communicationchamber 185, and stops there. At this time, control valve element 187,by means of rod portion 191 of control piston 190 opposes the forceprovided by spring 189, moves in the direction opposite that of controlchamber 180, and opens up bore 181. Additionally, during this time,valve element 173 of relief valve 164 covers up induction port 169 bymeans of the force provided by valve element spring 174.

After the aforementioned condition is shifted to a braking condition,when brake fluid pressure is generated from master cylinder 1, thisfluid pressure of master cylinder 1 acts on piston portion 193 andcoupling portion 192 of control valve 178 . As a result, control piston190 opposes the force of spring 196 and moves in the opposite directionto that of valve chamber 179. When this happens, control piston 190 isdesigned to come into contact with step portion 199 between largediameter chamber 184 and small diameter chamber 183. In this way, thecontact between control valve element 187 and rod portion 191 of controlpiston 190 is released. When this occurs, control valve element 187covers up bore 181 by means of the force provided by spring 189. On theother hand, at this time, because the fluid pressure of master cylinder1 acts on piston 175 which projects out from master cylindercommunication chamber 167, relief valve 164 is designed to maintainclosure of induction port 169 by means of the fluid pressure of mastercylinder 1 and force of spring 175.

In the above condition, in the case when antiskid control is beingcarried out, when the discharge pressure of pump 25 exceeds that of thecombined force of fluid pressure from master cylinder 1 to act on piston175 and the force provided by valve element spring 174, valve element173 of relief valve 164 moves towards master cylinder communicationchamber 167, opening up induction port 169. In doing this, surplusdischarge pressure of pump 25 is allowed to escape to reservoir 18 bymeans of first bypass circuit 45. As a result, the discharge pressurepump 25 to be delivered to pump communication port 15 of flow controlvalve 8, is designed to be controlled at approximately the same level asthe combined force of the pressure force of master cylinder 1 and thepredetermined force provided by valve element spring 174. Furthermore,at this time, the discharge pressure of pump 25 is designed to bedelivered to valve chamber 179 of control valve 178 via second bypasscircuit 126; however, because bore 181 is closed off by control valveelement 187, the circulation of this discharge pressure to mastercylinder 1 via second bypass circuit 126 is not carried out.

During the above antiskid control, after braking is released, when fluidpressure of master cylinder 1 decreases, the fluid pressure to act onpiston portion 193 and coupling portion 192 of control piston 190 isdesigned to also decrease. As a result, control piston 190, by means ofthe force provided by spring 196, moves in the valve chamber 179direction, and places piston portion 193 in contact with end portion 198of control chamber 180, as shown in FIG. 7 . In this manner, controlvalve element 187 opposes the force of spring 189, moves in thedirection opposite that of control chamber 180, and opens up bore 181.The residue liquid inside reservoir 18 taken in/discharged from pump 25is thus designed to return directly to master cylinder 1 via secondbypass circuit 126. Consequently, in a manner similar to that in thefifth embodiment, during antiskid control, when braking is released,because the brake fluid discharged to flow control valve 8 disappears,the brake fluid flowing to wheel cylinder 3 similarly disappears.Therefore, generation of the overshoot phenomenon does not occur, andfluid pressure of wheel cylinder 3 can be rapidly decreased in responseto the release of braking.

In the following, brake fluid pressure control apparatus according tothe seventh embodiment of the present invention will be explained withreference to FIGS. 8 and 9. Furthermore, in regard to the secondembodiment, the seventh embodiment differs primarily in one portion ofthe flow control valve, thus the following explanation will concentrateon this differing portion, omitting details on the parts similar to theapparatus according to the second embodiment denoted by identicalnumbers.

In brake fluid control apparatus 200 according to the seventhembodiment, master cylinder communication port 11 is designed at apredetermined diameter smaller than that of pump communication port 15.In this way, when spool 31 enters a moving state, first groove 37 isconstructed in a manner such that it communicates to pump communicationport 15 by its end portion opposite the direction of movement (the upperpart in FIG. 8), in a state in which it does not directly connect tomaster cylinder communication port 11.

Furthermore, during antiskid control, pump 25 is normally in a drivingstate. When spool 31 moves, first groove 37 of spool 31 is designed toconnect to pump communication port 15 by the end portion of first groove37 opposite the direction of movement. At this time, because thediameter of master cylinder communication port 11 is designed at apredetermined diameter smaller than that of pump communication port 15,master cylinder communication port 11 is designed to slightly connectvia clearance 201 formed from the outer periphery portion of spool 31between master cylinder communication port 11 and first groove 37, andthe inner periphery portion of cylinder 9 of casing 10, without directlyconnecting to first groove 37. As a result, the brake fluid dischargedfrom pump 25, at the time of depressurization with the opening ofelectromagnetic normally closed valve 20, flows from pump communicationport 15 to reservoir 18 at approximately a fixed flow amount via firstgroove 37, second aperture 39, upper portion aperture 32, interiororifice 34, lower portion aperture 33, and reservoir communication port14 by means of extraction at interior orifice 34. Additionally, duringclosing of electromagnetic first valve 20 and repressurization, brakefluid discharged from pump 25 flows from pump communication port 15 towheel cylinder 3 via first groove 37, second aperture 39, upper portionaperture 32, interior orifice 34, lower portion aperture 33, fourthaperture 44, third groove 43, and lower portion part 17 of wheelcylinder communication port 13, at approximately a fixed flow amount bymeans of extraction at interior orifice 34 . At the same time, a minuteportion of the brake fluid discharged from pump 25 is extracted by meansof clearance 201 formed from the aforementioned outer periphery portionof spool 31 and the inner periphery portion of casing 10, and isdesigned to return to master cylinder 1 at approximately a fixed flowamount (see FIG. 9).

Consequently, the aforementioned clearance 201 becomes a second orificeconnecting pump communication port 15 and master 20 cylindercommunication port 11, and prevents unpleasant pedal sensations such aspedal kickback. Moreover, there is no longer a need for the passagewayconnecting master cylinder communication port 11 and pump communicationport 15, and the outer orifice to be provided in casing 10. As a result,the entire body of brake fluid pressure control apparatus 200 can bemade more compact and the manufacturing cost can be lowered.

Moreover, in the present embodiment, relief valve 47 (see FIG. 4) isdesigned to control the discharge pressure to be delivered from pump 25to pump communication port 15 at a predetermined pressure level greaterthan the pressure force of master cylinder 1. Due to this, when thedischarge pressure of pump 25 is greater than the pressure force ofmaster cylinder 1, the difference between the brake fluid pressure ofmaster cylinder 1 and the brake fluid pressure delivered to flow controlvalve 8 via relief valve 47 becomes fixed. This brake fluid possessingthis difference in pressure is designed to pass through interior orifice34 and the aforementioned clearance 201. Consequently, fluctuations ofpressure force delivered to master cylinder 1 via the aforementionedclearance 201 can be effectively further prevented. Similarly, reliefvalve 47 is designed to prevent unnecessary rising of the brake fluidpressure between the discharging side of pump 25 and flow control valve8.

In the following, a modified example of the seventh preferred embodimentis described as shown in FIG. 10. Furthermore, this modified example isa unitary body formed from the aforementioned flow control valve 8 andelectromagnetic first valve 20, the individual constructions of whichare identical to that stated in the aforementioned embodiments.

Flow control valve 8 is inserted inside sleeve (casing) 202. Inside ofthis sleeve 202, master cylinder communication port 11, wheel cylindercommunication port 13, and pump communication port 15 are all providedin predetermined positions. This sleeve 202 is inserted into both spool31 and opening 204 of housing 203. Opening portion 205 of housing 203 isdesigned to be closed off by closing member 206, and sleeve 202 is fixedto housing 203. Master cylinder communication port 11 of sleeve 202 iscommunicated to channel 211 of housing 203, and in turn this channel 211is communicated to the master cylinder. Wheel cylinder communicationport 13 is communicated to channel 209 of housing 203 via filter 210 andthis channel 209 is in turn communicated to the wheel cylinder.Additionally, pump communication port 15 communicates to channel 207 ofhousing 203 via filter 208: this channel 207 communicates with the pump.Additionally, an opening portion 213 at the lower part of sleeve pumpport 202 in FIG. 10, is communicated to reservoir communication port 14which is enclosed in closing member 206; in this closing member 206, anelectromagnetic first valve 20 which communicates and cuts off channel214 which in turn is communicated to reservoir communication port 14 .This electromagnetic first valve 20 is constructed from armature 216, onwhich valve portion 215 which communicates and cuts off channel 214 isprovided. Electromagnetic portion 217 which by means of magnetizationmoves this armature 216 and communicates channel 214, and spring 218which, in the condition when electromagnetic portion 217 is notmagnetized, provides a force to armature 216, closes channel 214 usingarmature 216.

In the following, a brake fluid pressure control apparatus according tothe eighth embodiment of the present invention will be explained withreference to FIG. 11. Furthermore, in regards to the seventh embodiment,the eighth embodiment differs primarily in a portion of the spool of theflow control valve, thus the explanation will center mainly around thisdiffering portion, omitting explanations of portions similar to thatdescribed in the seventh embodiment as denoted by identical numbers.

On the outer periphery portion of spool 31 in flow control valve 8 ofbrake fluid pressure control apparatus 219 according to the eighthembodiment, at a predetermined distance higher than the first grooveportion 37, a V-shaped minute groove 220 is provided around the entirecircumference. This minute groove 220, when there is no action ofantiskid control and when spool 31 is in a motionless state, does notopen master cylinder communication port 11 and pump communication port15; when antiskid control is being carried out, and when spool 31 is ina moving state, this minute groove 220 opens, creating a minutecommunication between master cylinder communication port 11 and pumpcommunication port 15.

In this way, as shown in FIG. 11, during antiskid Control, when spool 31of control valve 8 moves, first groove 37, in the same manner as in theseventh embodiment, communicates to pump communication port 15 using thetip portion of spool 31 in the direction of movement. At the same timeas this, spool 31 becomes minutely communicated to the aforementionedmaster cylinder communication port 11 via clearance 201 between spool 31and master cylinder communication port 11. Together with this, minutegroove 220 minutely communicates pump communication port 15 and mastercylinder communication port 11.

Consequently, clearance 201 between master cylinder communication port11 and first groove 37, and minute groove 220 form a second orifice. Bymeans of this, clearance 201 and minute groove 220, a portion of brakefluid discharged from pump 25 to pump communication port 15 via reliefvalve 47 (see FIG. 4), is designed to be squeezed out, and returned tomaster cylinder 1 at approximately a fixed flow rate. As a result, in amanner similar to that for the seventh embodiment, unpleasant pedalkickback can be prevented, and there is no longer a necessity for achannel connecting master cylinder communication port 11 and pumpcommunication port 15 and exterior orifice to be provided in casing 10.Due to this, brake fluid pressure control apparatus 219 can be madecompact and manufacturing costs can be reduced.

Furthermore, because the size of this minute groove 220 can be easilychanged, modifications in the size of the flow path area over whichbrake fluid, passing through flow control valve 8 and returning tomaster cylinder 1, passes, can be carried out. That is namely,modification of the flow amount of brake fluid returning to mastercylinder 1, can be carried out. Consequently, in the case whenrecognition of the antiskid control state through a pedal is preferred,pedal kickback can be designed over a range in which unpleasantsensations do not occur. Additionally, due to the presence of thisminute groove 220, as shown in FIG. 11, even when for example spool 31is fixed, safety is an advantage since small communications of each portcan be maintained.

What is claimed is:
 1. A pressure control apparatus for anti-skid brakesystems of wheeled vehicles, comprising:a master cylinder for deliveringpressure by means of a brake fluid in accordance with an operation of abrake pedal; a wheel cylinder for exerting braking force to a wheel bymeans of brake fluid pressure, a normally closed valve for opening andclosing at decrease and increase of brake fluid pressure, respectively,a reservoir for receiving brake fluid at decrease of brake fluidpressure, a pump for charging with said brake fluid from said reservoirand for discharging said brake fluid, said pump having an intake sideand a discharge side, a flow valve including:A. a casing having,i. amaster cylinder communication port for communicating with said mastercylinder, ii. a wheel cylinder communication port for communicating withsaid wheel cylinder, iii. a reservoir communication port forcommunicating with said reservoir and said intake side of said pumpthrough said normally closed valve, and iv. a pump communication portfor communicating with said discharge side of said pump, B. a spoolmovable within said casing, and C. a spring for urging said spool towarda stationary position, wherein when said spool is at said stationaryposition, communication between said master cylinder communication portand said wheel cylinder communication port is enabled, and when saidspool is displaced from said stationary position due to a pressuredifference on both sides thereof resultant from opening of said normallyclosed valve, communication between said master cylinder communicationport and said wheel cylinder communication port is restricted, saidwheel cylinder communication port is communicated with said reservoircommunication port, and, in a state in which said normally closed valveis closed, an approximate fixed flow amount of said brake fluid fromsaid pump communication port to said wheel cylinder communication portis enabled, a control by-pass line for connecting said master cylinderand said discharge side of said pump, and a control valve provided onsaid control bypass line for closing the bypass line when brake fluidpressure is higher than a predetermined value, and for opening theby-pass line when brake fluid pressure is not higher than saidpredetermined value.
 2. A pressure control apparatus in accordance withclaim 1 which further comprises:a relief by-pass line connecting saiddischarge side of said pump and said reservoir, and a relief valveprovided on said relief by-pass line for allowing escape of excessivedischarge pressure.
 3. A pressure control apparatus in accordance withclaim 2, wherein said control valve and said relief valve are aligned inseries.
 4. A pressure control apparatus in accordance with claim 2,wherein said control valve comprises:a control piston for receivingbrake fluid pressure, a control spring urging said control pistonagainst said brake fluid pressure, a valve for opening and closing saidcontrol by-pass line, a valve spring for urging said valve in adirection of closing of said control by-pass path, and a bar for urgingsaid valve opposing said valve spring so as to open said control by-passline by means of the force of said control spring, and for, when saidcontrol piston receives brake pressure from said master cylinder andmoves against said control spring, releasing pressure to said valve soas to close said bypass line by means of said valve.
 5. A pressurecontrol apparatus in accordance with claim 4 in which said relief valvecomprises:an axial part provided on an opposite side of said controlpiston with respect to said bar, a valve member, on which said pumpdischarge pressure acts to open and close said relief by-pass line, anda valve member spring provided between said axial part and said valvemember, for urging said valve member in a direction of closing saidrelief by-pass line, and which is compressed when said control pistonreceives brake fluid pressure and moves in opposition to a force of saidcontrol spring.